Two toilets of the same model have different cleaning issues (persistent black gunk in rim jets and a hard-to-reach siphon jet stain) that cannot be fully cleaned with standard cleaner and brush, and

Two toilets of the same model have different cleaning issues (persistent black gunk in rim jets and a hard-to-reach siphon jet stain) that cannot be fully cleaned with standard cleaner and brush, and in-tank cleaning tablets damage flappers, requiring a plumber-safe alternative.